The tracking area update (TAU) procedure helps a mobility management entity (MME) know where a mobile device is located in a wireless communication network so that the mobile device can be paged efficiently. When the mobile device enters the coverage area of a new MME, the mobile device sends a TAU request to the new MME to notify the new MME of its change in location. The new MME must retrieve context information about the mobile device from the MME previously serving the mobile device. Thus the mobile device includes information identifying the previous MME in the TAU request sent to the new MME. After the new MME retrieves the context information for the mobile device from the old MME, the new MME sends the mobile device a TAU accept with identification information for the new MME.
Relay technologies have been considered to improve high data rate area coverage and to enable group mobility in Third Generation Partnership (3GPP) Universal Mobile Telecommunications Systems (UMTS) Long Term Evolution-Advanced (LTE-Advanced) networks. Such a network is also referred to as an Evolved Universal Terrestrial Radio Access Network (E-TRAN). A relay node (RN) is wirelessly connected to radio-access network (RAN) via a base station (eNB in 3GPP E-UTRAN). In the group mobility architecture, one or more mobile devices are connected to a mobile RN, which each mobile device perceives as a base station. The mobile RN may be installed on a vehicle such as train, bus or water vessel, or some other mobile entity on which one or more mobile devices reside. The mobile devices served by the mobile RN thus connect to the network via the mobile RN.
When a mobile device remains in a vehicle that supports group mobility, the mobile device is constantly connected to/camped on the mobile RN even when the vehicle moves about. Since there is no mobility such as cell reselection or handover observed by the mobile device, there is no need for the mobile device to send TAU requests and the mobile device will not receive TAU accept messages. However, as the entity on which the mobile RN moves about the network, handover is performed for the mobile RN to change the eNB serving the RN. Thus the MME serving the mobile RN may change. When the mobile device is handed over from the mobile RN to a different serving base station, the mobile device will not be able to provide the new serving base station/MME with the identity of the MME previously serving the mobile device via the mobile RN.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon a careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.